Selective stimulation systems and signal parameters for medical conditions

ABSTRACT

Devices, systems and methods are provided for targeted treatment of a variety of conditions, particularly conditions that are associated with or influenced by the nervous system, such as pain. Targeted treatment of such conditions is provided with minimal deleterious side effects, such as undesired motor responses or undesired stimulation of unaffected body regions. This is achieved by directly neuromodulating a target anatomy associated with the condition while minimizing or excluding undesired neuromodulation of other anatomies.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/688,546, filed Aug. 28, 2017 titled “SELECTIVE STIMULATION SYSTEMSAND SIGNAL PARAMETERS FOR MEDICAL CONDITIONS,” which is a continuationof U.S. patent application Ser. No. 15/231,555, filed Aug. 8, 2016titled “SELECTIVE STIMULATION SYSTEMS AND SIGNAL PARAMETERS FOR MEDICALCONDITIONS,” which is a continuation of U.S. patent application Ser. No.14/726,359, filed May 29, 2015 titled “SELECTIVE STIMULATION SYSTEMS ANDSIGNAL PARAMETERS FOR MEDICAL CONDITIONS,” which is a divisional of U.S.patent application Ser. No. 12/607,009, titled “SELECTIVE STIMULATIONSYSTEMS AND SIGNAL PARAMETERS FOR MEDICAL CONDITIONS,” filed Oct. 27,2009, which claims priority under 35 U.S.C. 119(e) to U.S. ProvisionalPatent Application No. 61/108,836, titled “SELECTIVE STIMULATION SYSTEMSAND SIGNAL PARAMETERS FOR PAIN MANAGEMENT”, filed Oct. 27, 2008, each ofwhich is herein incorporated by reference in its entirety.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH OR DEVELOPMENT

Not Applicable

REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAMLISTING APPENDIX SUBMITTED ON A COMPACT DISK

Not Applicable

BACKGROUND OF THE INVENTION

Pain of any type is the most common reason for physician consultation inthe United States, prompting half of all Americans to seek medical careannually. It is a major symptom in many medical conditions,significantly interfering with a person's quality of life and generalfunctioning. Diagnosis is based on characterizing pain in various ways,according to duration, intensity, type (dull, burning, throbbing orstabbing), source, or location in body. Usually if pain stops withouttreatment or responds to simple measures such as resting or taking ananalgesic, it is then called ‘acute’ pain. But it may also becomeintractable and develop into a condition called chronic pain in whichpain is no longer considered a symptom but an illness by itself.

The application of specific electrical energy to the spinal cord for thepurpose of managing pain has been actively practiced since the 1960s. Itis known that application of an electrical field to spinal nervoustissue can effectively mask certain types of pain transmitted fromregions of the body associated with the stimulated nervous tissue. Suchmasking is known as paresthesia, a subjective sensation of numbness ortingling in the afflicted bodily regions. Such electrical stimulation ofthe spinal cord, once known as dorsal column stimulation, is nowreferred to as spinal cord stimulation or SCS.

FIGS. 1A-1B illustrate conventional placement of an SCS system 10.Conventional SCS systems include an implantable power source orimplantable pulse generator (PG) 12 and an implantable lead 14. SuchIPGs 12 are similar in size and weight to cardiac pacemakers and aretypically implanted in the buttocks or abdomen of a patient P. Usingfluoroscopy, the lead 14 is implanted into the epidural space E of thespinal column and positioned against the dura layer D of the spinal cord5, as illustrated in FIG. 1B. The lead 14 is implanted either throughthe skin via an epidural needle (for percutaneous leads) or directly andsurgically through a mini laminotomy operation (for paddle leads orpercutaneous leads). A laminotomy is a neurosurgical procedure thatremoves part of a lamina of the vertebral arch. The laminotomy createsan opening in the bone large enough to pass one or more leads through.

FIG. 2 illustrates example conventional paddle leads 16 and percutaneousleads 18. Paddle leads 16 typically have the form of a slab of siliconrubber having one or more electrodes 20 on its surface. Exampledimensions of a paddle lead 16 are illustrated in FIG. 3. Percutaneousleads 18 typically have the form of a tube or rod having one or moreelectrodes 20 extending therearound. Example dimensions of apercutaneous lead 18 are illustrated in FIG. 4.

Implantation of a percutaneous lead 18 typically involves an incisionover the low back area (for control of back and leg pain) or over theupper back and neck area (for pain in the arms). An epidural needle isplaced through the incision into the epidural space and the lead isadvanced and steered over the spinal cord until it reaches the area ofthe spinal cord that, when electrically stimulated, produces a tinglingsensation (paresthesia) that covers the patient's painful area. Tolocate this area, the lead is moved and turned on and off while thepatient provides feedback about stimulation coverage. Because thepatient participates in this operation and directs the operator to thecorrect area of the spinal cord, the procedure is performed withconscious sedation.

Implantation of paddle leads 16 typically involves performing a minilaminotomy to implant the lead. An incision is made either slightlybelow or above the spinal cord segment to be stimulated. The epiduralspace is entered directly through the opening in the bone and a paddlelead 16 is placed over the region to stimulate the spinal cord. Thetarget region for stimulation usually has been located before thisprocedure during a spinal cord stimulation trial with percutaneous leads18.

Although such SCS systems have effectively relieved pain in somepatients, these systems have a number of drawbacks. To begin, asillustrated in FIG. 5, the lead 14 is positioned upon the spinal corddura layer D so that the electrodes 20 stimulate a wide portion of thespinal cord and associated spinal nervous tissue (as indicated byperimeter 21). The spinal cord is a continuous body and three spinallevels of the spinal cord are illustrated. For purposes of illustration,spinal levels are sub-sections of the spinal cord S depicting thatportion where the dorsal root DR and ventral root VR join the spinalcord S. The spinal nerve N divides into the dorsal root DR and thedorsal root ganglion DRG and the ventral nerve root VR each of whichfeed into the spinal cord S. Generally, the dorsal roots DR feed intothe posterior side of the spinal cord S and the ventral roots VR feedinto the anterior side of the spinal cord S. For simplicity, each levelshown illustrates the nerves of only one side and a normal anatomicalconfiguration would have similar nerves on the opposite side of thespinal cord.

FIG. 6 illustrates a cross-sectional view of the lead 14 of FIG. 5 at aspinal level. Thus, as shown, the lead 14 is positioned against the duralayer D near the midline of the spinal cord S. The electrode 20stimulates a wide portion of the spinal cord. In this example, the lead14 is a unidirectional paddle lead so the stimulation energy 15(indicated by perimeter 21) extends to one side of the lead 14.Significant energy 15 is utilized to penetrate the dura layer D andcerebral spinal fluid CSF to activate fibers in the spinal columnextending within the posterior side of the spinal cord S,post-synaptically to the dorsal roots. And, in cases of omnidirectionalleads, even more energy may be required due to loss of energy that isdirected away from the target. Sensory spinal nervous tissue, or nervoustissue from the dorsal nerve roots, transmit pain signals. Therefore,such stimulation is intended to block the transmission of pain signalsto the brain with the production of a tingling sensation (paresthesia)that masks the patient's sensation of pain. However, excessive tinglingmay be considered undesirable. Further, the energy 15 also typicallypenetrates the anterior side of the spinal cord 5, stimulating theventral horns, and consequently the ventral roots extending within theanterior side of the spinal cord S. Motor spinal nervous tissue, ornervous tissue from ventral nerve roots, transmits muscle/motor controlsignals. Therefore, electrical stimulation by the lead 14 often causesundesirable stimulation of the motor nerves in addition to the sensoryspinal nervous tissue. The result is undesirable muscle contraction.

Because the electrodes span several levels and because they stimulatemedial to spinal root entry points, the generated stimulation energy 15stimulates or is applied to more than one type of nerve tissue on morethan one level. Moreover, these and other conventional, non-specificstimulation systems also apply stimulation energy to the spinal cord andto other neural tissue beyond the intended stimulation targets. As usedherein, non-specific stimulation refers to the fact that the stimulationenergy is provided to multiple spinal levels including the nerves andthe spinal cord generally and indiscriminately. This is the case evenwith the use of programmable electrode configurations wherein only asubset of the electrodes are used for stimulation. In fact, even if theepidural electrode is reduced in size to simply stimulate only onelevel, that electrode will apply stimulation energy non-specifically andindiscriminately (i.e. to many or all nerve fibers and other tissues)within the range of the applied energy.

Therefore, improved stimulation systems, devices and methods are desiredthat enable more precise and effective delivery of stimulation energy.At least some of these objectives will be met by the present invention.

BRIEF SUMMARY OF THE INVENTION

The present invention provides devices, systems and methods for targetedtreatment of a variety of conditions, particularly conditions that areassociated with or influenced by the nervous system. Examples of suchconditions include pain, itching, Parkinson's Disease, MultipleSclerosis, demylenating movement disorders, spinal cord injury, asthma,chronic heart failure, obesity and stroke (particularly acute ischemia),to name a few. The present invention provides for targeted treatment ofsuch conditions with minimal deleterious side effects, such as undesiredmotor responses or undesired stimulation of unaffected body regions.This is achieved by directly neuromodulating a target anatomy associatedwith the condition while minimizing or excluding undesiredneuromodulation of other anatomies. In most embodiments, neuromodulationcomprises stimulation, however it may be appreciated thatneuromodulation may include a variety of forms of altering or modulatingnerve activity by delivering electrical or pharmaceutical agentsdirectly to a target area. For illustrative purposes, descriptionsherein will be provided in terms of stimulation and stimulationparameters, however, it may be appreciated that such descriptions arenot so limited and may include any form of neuromodulation andneuromodulation parameters.

Typically, the systems and devices are used to stimulate portions ofneural tissue of the central nervous system, wherein the central nervoussystem includes the spinal cord and the pairs of nerves along the spinalcord which are known as spinal nerves. The spinal nerves include bothdorsal and ventral roots which fuse in the intravertebral foramen tocreate a mixed nerve which is part of the peripheral nervous system. Atleast one dorsal root ganglion (DRG) is disposed along each dorsal rootprior to the point of mixing. Thus, the neural tissue of the centralnervous system is considered to include the dorsal root ganglions andexclude the portion of the nervous system beyond the dorsal rootganglions, such as the mixed nerves of the peripheral nervous system.Typically, the systems and devices of the present invention are used tostimulate one or more dorsal root ganglia, dorsal roots, dorsal rootentry zones, or portions thereof, while minimizing or excludingundesired stimulation of other tissues, such as surrounding or nearbytissues, ventral root and portions of the anatomy associated with bodyregions which are not targeted for treatment. However, it may beappreciated that stimulation of other tissues are contemplated.

In a first aspect of the present invention, a system is providedstimulating at least a portion of a target dorsal root. In someembodiments, the system comprises a lead having at least one electrode,wherein the lead is configured to be positioned so that at least one ofthe at least one electrodes is able to stimulate the at least a portionof the target dorsal root, and an implantable pulse generatorconnectable with the lead, wherein the generator provides a stimulationsignal to the lead which has an energy below an energy threshold forstimulating a ventral root associated with the target dorsal root whilethe lead is so positioned. In some embodiments, the at least a portionof the target dorsal root comprises a dorsal root ganglion.

In some embodiments, the stimulation signal has a current amplitude ofless than or equal to approximately 4 mA. Optionally, the currentamplitude may be less than or equal to approximately 800 μA. In someinstances the at least one of the at least one electrodes has an averageelectrode surface area of less than or equal to approximately 6 mm².Optionally, the average electrode surface area is less than or equal toapproximately 4 mm².

In some embodiments, the system further comprises a second lead havingat least one electrode, wherein the second lead is configured to bepositioned so that at least one of its electrodes is able to stimulateat least a portion of a second target dorsal root, and wherein thesecond lead is connectable to the implantable pulse generator whichprovides a stimulation signal to the second lead, wherein thestimulation signal to the second lead has an energy below an energythreshold for stimulating a ventral root associated with the secondtarget dorsal root while the second lead is so positioned. In someinstances, the target dorsal root and the second target dorsal root areon different spinal levels. Optionally, the stimulation signal to thelead and the stimulation signal to the second lead are different.

In a second aspect of the present invention, a system is provided forstimulating a target neural tissue of the central nervous system. Insome embodiments, the system comprises a lead having at least oneelectrode, wherein the lead is configured to be positioned so that atleast one of the at least one electrodes is able to stimulate the targetneural tissue, and an implantable pulse generator connectable with thelead, wherein the generator provides a stimulation signal having acurrent amplitude which is less than 100 μA. Typically, the targetspinal neural tissue comprises a dorsal root ganglion.

In a third aspect of the present invention, a system is provided forstimulating at least a portion of a target dorsal root, wherein thesystem includes a lead having at least one electrode, and wherein thelead is configured to be positioned so that at least one of the at leastone electrodes is able to stimulate the at least a portion of the targetdorsal root when provided a stimulation signal The system also includesan implantable pulse generator connectable with the lead, wherein thegenerator provides the stimulation signal which has an energy of lessthan approximately 100 nJ per pulse. In some embodiments, thestimulation signal has an energy of less than approximately 50 nJ perpulse. Optionally, the stimulation signal may have an energy of lessthan approximately 10 nJ per pulse. Typically, the at least a portion ofthe target dorsal root comprises a dorsal root ganglion.

In a fourth aspect of the present invention, a system is provided forstimulating at least a portion of a target dorsal root, wherein thesystem includes a lead having at least one electrode, wherein the leadis configured to be positioned so that at least one of the at least oneelectrodes is able to stimulate the at least a portion of the targetdorsal root when provided a stimulation signal. The system also includesan implantable pulse generator connectable with the lead, wherein thegenerator provides a stimulation signal which has a current amplitude ofless than 4 mA.

In a fifth aspect of the present invention, a system is provided forstimulating at least a portion of a target dorsal root, wherein thesystem includes a lead having at least one electrode, and wherein thelead is configured so that at least one of the at least one electrodesis positionable on or near the at least a portion of the target dorsalroot. The system also includes an implantable pulse generatorconnectable with the lead, wherein the generator provides a stimulationsignal to the at least one of the at least one electrode whichselectively stimulates the at least a portion of the target dorsal rootdue to at least one signal parameter. In some embodiments, the at leastone signal parameter includes current amplitude. In these embodiments,the current amplitude may be less than or equal to approximately 4 mA.Likewise, in some embodiments, the at least one signal parameterincludes pulse width and the pulse width is less than 500 μs. Typically,the at least a portion of the target dorsal root comprises a dorsal rootganglion.

In a sixth aspect of the present invention, a system for stimulating atarget dorsal root ganglion is provided comprising a lead having atleast one electrode, wherein the lead is configured so that at least oneof the at least one electrodes is positionable on or near the targetdorsal root ganglion. The system also includes an implantable pulsegenerator connectable with the lead, wherein the generator energizes theat least one of the at least one electrodes which selectively stimulatesthe target dorsal root ganglion due to its proximity to the targetdorsal root ganglion.

In a seventh aspect of the present invention, a system is provided forstimulating a target neural tissue of the central nervous systemcomprising a lead having at least one electrode, wherein the lead isconfigured to be positioned so that at least one of the at least oneelectrodes is able to stimulate the target neural tissue, and animplantable pulse generator connectable with the lead, wherein thegenerator provides a stimulation signal having a current amplitude whichis adjustable in increments of 50 μA or less. In some embodiments, thecurrent amplitude is adjustable in increments of 25 μA or less.

In another aspect of the present invention, a method is provided forstimulating at least a portion of a target dorsal root comprisingpositioning a lead having at least one electrode so that at least one ofthe at least one electrodes is on or near the at least a portion of thetarget dorsal root, and energizing at least one of the at least oneelectrodes with an energy level below an energy threshold forstimulating a ventral root associated with the target dorsal root whilethe lead is so positioned. In some embodiments, energizing comprisesproviding a stimulation signal having a current amplitude of less thanor equal to approximately 4 mA. Optionally, the current amplitude isless than or equal to approximately 1.0 mA. In some embodiments,positioning the lead comprises advancing the lead using an epiduralapproach. In these embodiments, positioning the lead may compriseadvancing the lead using an antegrade approach or a retrograde approach.It may also be appreciated that the lead may be positioned by advancingthe lead using transforamenal approach from outside of the spinalcolumn. Typically, the at least a portion of the target dorsal rootcomprises a dorsal root ganglion. In some embodiments, the averageelectrode surface area is less than or equal to approximately 4 mm².

In some embodiments, the method further comprises positioning a secondlead having at least one electrode so that at least one of its at leastone electrodes is on or near at least a portion of a second targetdorsal root, and energizing at least one of the at least one electrodesof the second lead with an energy level below an energy threshold forstimulating a ventral root associated with the second target dorsal rootwhile the second lead is so positioned. In some embodiments, the targetdorsal root and the second target dorsal root are on different spinallevels. Likewise, in some embodiments, the energy level of the lead andthe second lead are different.

In another aspect of the present invention, a method of stimulating atarget spinal neural tissue within an epidural space is providedcomprising positioning a lead having at least one electrode, so that atleast one of the at least one electrodes is able to stimulate the targetspinal neural tissue, and energizing the at least one of the at leastone electrodes with a stimulation signal which has a current amplitudewhich is less than 100 μA.

In another aspect of the present invention, a method of stimulating atleast a portion of a target dorsal root is provided comprisingpositioning a lead having at least one electrode, so that at least oneof the at least one electrodes is able to stimulate the at least aportion of the target dorsal root and energizing the at least one of theat least one electrodes with a stimulation signal which has an energy ofless than approximately 100 nJ per pulse.

In another aspect of the present invention, a method for stimulating atleast a portion of a target dorsal root is provided comprisingpositioning a lead having at least one electrode, so that at least oneof the at least one electrodes is able to stimulate the at least aportion of the target dorsal root and energizing the at least one of theat least one electrodes with a stimulation signal which has a currentamplitude of less than 4 mA.

In another aspect of the present invention, a method for stimulating atleast a portion of the target dorsal root is provided comprisingpositioning a lead having at least one electrode so that at least one ofthe at least one electrode is on or near the at least a portion of thetarget dorsal root and energizing at least one of the at least oneelectrodes with a stimulation signal which selectively stimulates the atleast a portion of the target dorsal root due to at least one signalparameter.

In yet another aspect of the present invention, a method is provided forstimulating a target neural tissue of the central nervous systemcomprising positioning a lead having at least one electrode so that atleast one of the at least one electrode is able to stimulate the targetneural tissue, and energizing at least one of the at least oneelectrodes with a stimulation signal having a current amplitude which isadjustable in increments of 50 μA or less.

Due to variability in patient anatomy, pain profiles, pain perceptionand lead placement, to name a few, signal parameter settings will likelyvary from patient to patient and from lead to lead within the samepatient. Signal parameters include voltage, current amplitude, pulsewidth and repetition rate, to name a few. In some embodiments of thestimulation system of the present invention, the voltage provided is inthe range of approximately 0-7 volts. In some embodiments, the currentamplitude provided is less than approximately 4 mA, particularly in therange of approximately 0.5-2 mA, more particularly in the range ofapproximately 0.5-1.0 mA, 0.1-1.0 mA. or 0.01-1.0 mA. Further, in someembodiments, the pulse width provided is less than approximately 2000μs, particularly less than approximately 1000 μs, more particularly lessthan approximately 500 μs, or more particularly 10-120 μs. And, in someembodiments, the repetition rate is in the range of approximately 2-120Hz, up to 200 Hz or up to 1000 Hz.

Typically, stimulation parameters are adjusted until satisfactoryclinical results are reached. Thus, there is an envelope of stimulationparameter value combinations between the threshold for DRG stimulationand ventral root stimulation for any given lead positioned in proximityto any given DRG per patient. The specific combinations or possiblecombinations that could be used to successfully treat the patient aretypically determined perioperatively in vivo and postoperatively ex vivoand depend on a variety of factors. One factor is lead placement. Thecloser the desired electrodes are to the DRG the lower the energyrequired to stimulate the DRG. Other factors include electrodeselection, the anatomy of the patient, the pain profiles that are beingtreated and the psychological perception of pain by the patient, to namea few. Over time, the parameter values for any given lead to treat thepatient may change due to changes in lead placement, changes inimpedance or other physical or psychological changes. In any case, theenvelope of parameter values is exceedingly lower than those ofconventional stimulation systems which require energy delivery of atleast an order of magnitude higher to treat the patient's paincondition.

Given the lower ranges of parameter values, the granularity of controlis also smaller in comparison to conventional stimulation systems. Forexample, current in a conventional stimulation system is typicallyadjustable in increments of 0.1 mA. In some embodiments of the presentinvention, this increment is larger than the entire range of currentamplitude values that may be used to treat the patient. Thus, smallerincrements are needed to cycle through the signal parameter values todetermine the appropriate combination of values to treat the condition.In some embodiments, the system of the present invention providescontrol of current amplitude at a resolution of approximately 25 μA,particularly when using a current amplitude under, for example, 2 mA,however it may be appreciated that smaller increments may be used suchas approximately 10 μA, 5 μA or 1 μA. In other embodiments, control ofcurrent amplitude is provided at a resolution of approximately 50 μA,particularly when using a current amplitude of, for example, 2 mA orgreater. It may be appreciated that such a change in resolution mayoccur at other levels, such as 1 mA. Similarly, voltage in aconventional stimulation system is typically adjustable in increments of100 mV. In contrast, some embodiments of the present invention providecontrol of voltage at a resolution of 50 mV. Likewise, some embodimentsof the present invention provide control of pulse width at a resolutionof 10 μs. Thus, it may be appreciated that the present inventionprovides a high granularity of control of stimulation parameters due tothe low ranges of parameter values.

It may be appreciated that in some instances even lower levels of energymay be used to successfully treat a patient using the stimulation systemof the present invention. The closer a lead is positioned to a targetDRG, the lower the level of energy that may be needed to selectivelystimulate the target DRG. Thus, signal parameter values may be lowerthan those stated herein with correspondingly higher granularity ofcontrol.

Such reductions in energy allows a reduction in electrode size, amongother benefits. In some embodiments, the average electrode surface areais approximately 1-6 mm², particularly approximately 2-4 mm², moreparticularly 3.93 mm², whereas conventional spinal cord stimulatorstypically have a much larger average electrode surface area, such as 7.5mm², for some leads or 12.7 mm², for traditional paddle leads. Likewise,in some embodiments an average electrode length is 1.25 mm whereasconventional spinal cord stimulators typically have an average electrodelength of 3 mm. Such reduced electrode sizing allows more intimatepositioning of the electrodes in the vicinity of the DRG and allows forIPGs having different control and performance parameters for providingdirect and selective stimulation of a targeted neural tissue,particularly the DRG. In addition, in some embodiments the overalldimensions of one or more electrodes and the spacing of the electrodesis selected to match or nearly match the overall dimensions or size ofthe stimulation target.

Effective treatment of a condition may be achieved by directlystimulating a target anatomy associated with the condition whileminimizing or excluding undesired stimulation of other anatomies. Whensuch a condition is limited to or primarily affects a single dermatome,the present invention allows for stimulation of a single dermatome orregions within a dermatome (also referred to as subdermatomalstimulation).

In one aspect of the present invention, a method of treating a conditionassociated with a spinal neural tissue is provided, wherein thetreatment is applied substantially within a single dermatome. In someembodiments, the method comprises positioning a lead having at least oneelectrode so that at least one of the at least one electrodes is inproximity to the spinal neural tissue within an epidural space, andenergizing the at least one of the at least one electrodes so as tostimulate the spinal neural tissue causing a treatment effect within thesingle dermatome while maintaining body regions outside of the singledermatome substantially unaffected. In some embodiments, energizing theat least one electrode comprises energizing the at least one of the atleast one electrode so as to stimulate the spinal neural tissue causinga treatment affect within a particular body region within the singledermatome while maintaining body regions outside of the particular bodyregion substantially unaffected. Typically, the spinal neural tissuecomprises a dorsal root ganglion and the treatment effect comprisesparesthesia. In some embodiments, the particular body region comprises afoot.

In another aspect of the present invention, a method of treating acondition of a patient is provided, wherein the condition is associatedwith a portion of a dorsal root ganglion and is not substantiallyassociated with other portions of the dorsal root ganglion. In someembodiments, the method comprises positioning a lead having at least oneelectrode so that at least one of the at least one electrode resides inproximity to the portion of a dorsal root ganglion, and providing astimulating signal to the at least one of the at least one electrode soas to stimulate the portion of the dorsal root ganglion in a manner thataffects the condition while not substantially stimulating the otherportions. In some embodiments, the condition comprises pain. In suchembodiments, affecting the condition may comprise alleviating the painwithout causing a perceptible motor response.

In some embodiments, the condition is sensed by a patient at a locationwithin a dermatome, and the other portions of the dorsal root ganglionare associated with other locations within the dermatome. It may beappreciated, that the stimulating signal may have a current amplitude ofless than or equal to approximately 4 mA. Optionally, the stimulatingsignal may have current amplitude of less than or equal 1 mA. Typically,positioning the lead comprises advancing the lead using an epiduralapproach but is not so limited.

In another aspect of the present invention, a method of providingsubdermatomal stimulation is provided comprising positioning a leadhaving at least one electrode so that at least one of the at least oneelectrode resides near a dorsal root ganglion within a dermatome, andproviding a stimulating signal to the at least one of the at least oneelectrode so as to stimulate the dorsal root ganglion in a manner whichaffects a condition in a subdermatomal region of the dermatome.

In another aspect of the present invention, a system is provided forstimulating a portion of a dorsal root ganglion, wherein the portion ofthe dorsal root ganglion is associated with a particular region within adermatome. In some embodiments, the system comprises a lead having atleast one electrode, wherein the lead is configured to be positioned sothat at least one of the at least one electrode is able to stimulate theportion of the dorsal root ganglion, and a pulse generator connectablewith the lead, wherein the generator provides a stimulation signal tothe at least one of the at least one electrode which stimulates theportion of the dorsal root ganglion to cause an effect within theparticular region of the dermatome.

In some embodiments, the combination of the at least one of the at leastone electrode and the stimulation signal creates an electric fieldhaving a shape which allows for stimulation of the portion of the dorsalroot ganglion while substantially excluding other portions of the dorsalroot ganglion. In some embodiments, the at least one of the at least oneelectrode comprises two electrodes spaced 0.250 inches apart fromapproximate center to center of each electrode. In some embodiments,stimulation signal has a current amplitude of less than or equal toapproximately 4 mA. Optionally, the stimulating signal may have acurrent amplitude of less than or equal 1 mA. In some embodiments, thestimulation signal has an energy of less than approximately 100 nJ perpulse.

In another aspect of the present invention, a system for providingsubdermatomal stimulation within a patient is provided comprising a leadhaving at least one electrode, wherein the lead is configured so thatthe at least one electrode is positionable in proximity to a dorsal rootganglion associated with a dermatome, and a pulse generator connectablewith the lead. In some embodiments, the generator provides a firststimulation signal to at least one of the at least one electrode tocreate a first electric field which stimulates the dorsal root ganglioncausing a first effect within a first body region of the dermatome andthe generator provides a second stimulation signal to at least one ofthe at least one electrode to create a second electric field whichstimulates the dorsal root ganglion causing a second effect within asecond body region of the dermatome. In some instance, the first andsecond stimulation signals have different stimulation parameters. Insome embodiments, the at least one of the at least one electrodesreceiving the first stimulation signal differs from the at least one ofthe at least one electrodes receiving the second stimulation signal.

In some embodiments, the first and second electric fields have differentshapes. Likewise, the first and second electric fields may havedifferent sizes. In some embodiments, the first effect comprises relieffrom pain. In some embodiments, the first body region resides along afoot of the patient and the second body region resides along a back ofthe patient.

In yet another aspect of the present invention, a method for providingsubdermatomal stimulation within a patient is provided comprisingpositioning a lead having at least one electrode in proximity to adorsal root ganglion associated with a dermatome, applying a stimulationsignal to the at least one electrode which stimulates the dorsal rootganglion causing an effect within a first body region of the dermatome,and repositioning the lead along the dorsal root ganglion so that theapplication of the stimulation signal to the least one electrodestimulates the dorsal root ganglion to cause a second effect within asecond body region of the dermatome. In some embodiments, the firsteffect comprises relief from pain. In some embodiments, the first bodyregion resides along a foot of the patient and the second body regionresides along a back of the patient.

Other objects and advantages of the present invention will becomeapparent from the detailed description to follow, together with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1B, 2, 3, 4, 5, 6 illustrate prior art.

FIG. 7 illustrates an embodiment of a stimulation system of the presentinvention.

FIG. 8 provides a perspective view of an embodiment of an implantablepulse generator of the present invention.

FIG. 9 illustrates the IPG of FIG. 8 with a portion of the housingremoved to reveal the internal components.

FIG. 10 provides a schematic block diagram of printed circuit boardswhich are part of the electronic circuitry of one embodiment of the IPG.

FIG. 11 illustrates at least one external programming devicecommunicating with the IPG using telemetry.

FIG. 12 illustrates an example of possible parameters of a stimulationsignal which can be varied.

FIG. 13 is a simplified block diagram that illustrates possiblecomponents or the electronic circuitry of the IPG.

FIG. 14 is a simplified block diagram that illustrates possiblecomponents of an external programmer, such as a clinical programmer.

FIG. 15A provides a perspective expanded view of an embodiment of aclinical programmer.

FIG. 15B and FIG. 15C illustrate embodiments of screenshots of aclinical programmer.

FIG. 16 is a simplified block diagram that illustrates possiblecomponents of another external programmer, such as a patient programmer.

FIG. 17 illustrates example placement of the leads of the embodiment ofFIG. 7 within the patient anatomy.

FIG. 18 illustrates a cross-sectional view of an individual spinal levelshowing a lead of the stimulation system positioned near a target DRG.

FIG. 19A illustrates an embodiment of a trace representing a stimulationsignal of the present invention and FIG. 19B illustrates an embodimentof a corresponding trace showing the voltage response to a compleximpedance stimulating biological tissue.

FIG. 20A illustrates an embodiment of a trace representing an examplestimulation signal of a conventional spinal cord stimulator and FIG. 20Billustrates an embodiment of a corresponding trace showing the voltageresponse to a complex impedance stimulating biological tissue.

FIG. 21 illustrates data indicating the stimulation signal parameterswhich selectively targeted the DRG wherein there is an energy thresholdin which the DRG is stimulated which is below the energy threshold inwhich the ventral root is stimulated.

FIG. 22 illustrates the dermatomal arrangement or “map” of dermatomesalong a patient.

FIG. 23 schematically illustrates DRGs on various spinal levels withassociated body regions that may be affected by selective stimulation ofthe individual DRGs.

FIG. 24A illustrates the patient from the back, including the dermatomesof the lower body and a schematic representation of the general area ofthe DRGs, and FIG. 24B illustrates the patient from the front, includingthe dermatomes of the lower body.

FIG. 25 schematically illustrates selective stimulation of a DRGaccording to aspects of the present invention.

FIGS. 26A, 26B, 26C, 26D illustrate perspective views of a leadstimulating a portion of a DRG to affect a specific region within adermatome.

FIG. 27 and FIG. 28 provide tables of clinical data from Patient No. 1and Patient No. 2 respectively.

DETAILED DESCRIPTION OF THE INVENTION

In some embodiments, a target DRG is stimulated with a lead having atleast one electrode thereon. The lead is advanced through the patientanatomy so that the at least one electrode is positioned on, near orabout the target DRG. The lead is sized and configured so that theelectrode(s) are able to minimize or exclude undesired stimulation ofother anatomies. Such configuration may include a variety of designfeatures, including signal parameters, which will be described herein.

FIG. 7 illustrates an embodiment of an implantable stimulation system100 of the present invention. The system 100 includes an implantablepulse generator (IPG) 102 and at least one lead 104 connectable thereto.In preferred embodiments, the system 100 includes four leads 104, asshown, however any number of leads 104 may be used including one, two,three, four, five, six, seven, eight, up to 58 or more. Each lead 104includes at least one electrode 106. In preferred embodiments, each lead104 includes four electrodes 106, as shown, however any number ofelectrodes 106 may be used including one, two, three, four five, six,seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, fifteen,sixteen or more. Each electrode can be configured as off, anode orcathode. In some embodiments, even though each lead and electrode areindependently configurable, at any given time the software ensures onlyone lead is stimulating at any time. In other embodiments, more than onelead is stimulating at any time, or stimulation by the leads isstaggered or overlapping.

Referring again to FIG. 7, the IPG 102 includes electronic circuitry 107as well as a power supply 110, e.g., a battery, such as a rechargeableor non-rechargeable battery, so that once programmed and turned on, theIPG 102 can operate independently of external hardware. In someembodiments, the electronic; circuitry 107 includes a processor 109 andprogrammable stimulation information in memory 108.

FIG. 8 provides a perspective view of an embodiment of an IPG 102 of thepresent invention. Here the electronic circuitry 107 and power supply110 are enclosed in a housing 105 (also referred to as a “case” or“can”). It may be appreciated, that alternatively, the power supply maybe located outside of the housing 105, such as within an external devicewhich supplies power to the IPG 102, such as via inductive coupling, RFor photoactivation. In some embodiments, the IPG 102 as a volume notexceeding approximately 32 cc, a thickness not exceeding approximately1.2 cm or a weight not exceeding approximately 30 g. It may beappreciated that in other embodiments, the IPG 102 has a volume notexceeding approximately, 0.2, 5, 10, 15, 20, 30, 40, 50, 60 or 70 cc.The IPG 102 may have a variety of shapes, including an oval, circular,rounded square or rounded rectangular shape. In some embodiments, theIPG 102 has a height of approximately 61 mm, a width of approximately 48mm and a thickness of approximately 11 mm.

In some embodiments, the housing 105 of the IPG 102 is electricallyconductive. In such embodiments, the housing 105 can act as anelectrode, as explained in more detail below. The at least one electrode106 is electrically coupled to the electronic circuitry 107 by couplingthe lead 104 to a connector 111 of the IPG 102. In this embodiment, eachlead 104 is insertable into a separate port 115 in the IPG 102 toprovide electrical connection to each lead 104.

FIG. 9 illustrates the components within the IPG 102 of FIG. 8. In thisembodiment, the internal components include a power supply 110,electronic circuitry 107, an antenna 132, and a lead connector 111. Inthis embodiment, the electronic circuitry 107 includes three printedcircuit boards to allow the circuitry to reside in a small space. FIG.10 provides a schematic block diagram of these boards, which include anRF board 136, an MCU board 138 and an electrode board 140. The MCU boardincludes a microcontroller unit (MCU) which is a small computer on asingle integrated circuit comprising a CPU combined with supportfunctions such as a crystal oscillator, timers, serial and analog I/Oetc. Program memory, such as in the form of NOR flash or OTP ROM, mayalso be included on the chip, as well as RAM. It may be appreciated thatthe electronic circuitry 107 may include other arrangements andcomponents.

Referring to FIG, 11, the IPG 102 is turned on and off and programmed togenerate the desired stimulation pulses from at least one externalprogramming device using telemetry, such as transcutaneouselectromagnetic or RF links or a transmitting coil. In some embodiments,an RF link is used which complies with the MICS standard. This standardallocates a 402-405 MHz frequency spectrum intended for implantablemedical devices. In other embodiments, the RF link utilizes a frequencyof 400 MHz or greater. In still other embodiments, the RF link utilizesa frequency of 2.45 GHz. In some embodiments, telemetry is initiated bya magnet within or associated with the external programmer. The magnetactuates a magnetic sensor in the implanted IPG 102 when placed on theskin directly over the implant or within a suitable range of theimplant. In addition, in some embodiments, the IPG 102 sniffs on allchannels for communication attempts by external programmers. In someembodiments, such sniffing occurs over at predetermined intervals, suchas every 10 min, and such intervals can be programmable. This is abackup communication link should the IPG fail to detect the magnet.Should the IPG detect the presence of an external programmer, the IPGtypically responds to the programmer within thirty seconds, 15 secondsor less.

In some embodiments, the at least one external programming devicecomprises a clinical programmer 200 and a patient programmer 300. Theclinical programmer 200 is used to program the stimulation informationof the IPG 102, as determined by the clinician or investigator. Thestimulation information includes signal parameters such as voltage,current, pulse width, repetition rate, and burst rates. FIG. 12illustrates an example of possible parameters of a stimulation signalwhich may be varied. Using embodiments of the present invention, theamplitude, current, pulse width and repetition rate (also referred to asfrequency) which provide the optimal therapeutic result can bedetermined. It may be appreciated that a constant current with avariable amplitude may be used, or a constant amplitude with a variablecurrent may be used.

Referring back to FIG. 11, the patient programmer 300 allows the patientto adjust the stimulation settings of the IPG 102 within limits presetby the clinician. The patient programmer 300 also allows the patient toturn stimulation off, if necessary. The clinical and patient programmers200, 300 are portable, hand-held devices that can be plugged into apower outlet or powered by an internal battery. The battery is typicallyrechargeable using a power supply and a power outlet. In someembodiments, the programmers 200, 300 contain an internal magnet toinitiate communication with the IPG 102. The patient programmer 300 isdesigned to be easy to use and establishes two-way communication withthe IPG 102 to control the stimulation. Together the implantablestimulation system 100, clinical programmer 200 and patient programmer300 form a system 1000 which operates to provide personalized treatmentfor each patient, as will be described in more detail below.

It may be appreciated that the embodiments of FIGS, 8, 9, 10, 11 are forillustrative purposes, wherein the components may vary. For example,FIG. 13 is a simplified block diagram that illustrates possiblecomponents of the electronic circuitry of the IPG. In this embodiment,the electronic circuitry 418 is shown as including a battery 430, pulsegenerator 432, a controller 434, a switch device 436, telemetrycircuitry 436 and memory 439.

The battery 430 can be used to power the various other components of theelectronic circuitry 418. Further, the battery 430 can be used togenerate stimulation pulses. As such, the battery can be coupled to thepulse generator 432, the controller 434, the switch device 436, thetelemetry circuitry 438 and the memory 439. A voltage regulator (notshown) can step up or step down a voltage provided by the battery 430 toproduce one or more predetermined voltages useful for powering suchcomponents of the electronic circuitry 418. Additional electroniccircuitry, such as capacitors, resistors, transistors, and the like, canbe used to generate stimulation pulses, as is well known in the art.

The pulse generator 432 can be coupled to electrodes 106 of the lead(s)104 via the switch device 436. The pulse generator 432 can be a single-or multi-channel pulse generator, and can be capable of delivering asingle stimulation pulse or multiple stimulation pulses at a given timevia a single electrode combination or multiple stimulation pulses at agiven time via multiple electrode combinations. In one embodiment, thepulse generator 432 and the switch device 136 are configured to deliverstimulation pulses to multiple channels on a time-interleaved basis, inwhich case the switch device 436 time division multiplexes the output ofpulse generator 432 across different electrode combinations at differenttimes to deliver multiple programs or channels of stimulation energy tothe patient.

The controller 434 can control the pulse generator 432 to generatestimulation pulses, and control the switch device 436 to couple thestimulation energy to selected electrodes. More specifically, thecontroller 434 can control the pulse generator 432 and the switch device436 to deliver stimulation energy in accordance with parametersspecified by one or more stimulation parameter sets stored within thememory 439. Exemplary programmable parameters that can be specifiedinclude the pulse amplitude, pulse width, and pulse rate (also known asrepetition rate or frequency) for a stimulation waveform (also known asa stimulation signal). Additionally, the controller 434 can control theswitch device 436 to select different electrode configurations fordelivery of stimulation energy from the pulse generator 432. In otherwords, additional programmable parameters that can be specified includewhich electrodes 106 of which lead(s) 104 are to be used for deliveringstimulation energy and the polarities of the selected electrodes 106.Each electrode 106 can be connected as an anode (having a positivepolarity), a cathode (having a negative polarity), or a neutralelectrode (in which case the electrode is not used for deliveringstimulation energy, i.e., is inactive). A set of parameters can bereferred to as a stimulation parameter set since they define thestimulation therapy to be delivered to a patient. One stimulationparameter set may be useful for treating a condition in one location ofthe body of the patient, while a second stimulation parameter set may beuseful for treating a condition in a second location. It may beappreciated that each of the electrodes on an individual lead mayprovide a signal having the same signal parameters or one or moreelectrodes on the lead may provide a signal having differing signalparameters. Likewise, an individual electrode may provide a signalhaving differing signal parameters over time.

The controller 434 can include a microprocessor, a microcontroller, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field-programmable gate array (FPGA), a state machine,or similar discrete and/or integrated logic circuitry. The switch device436 can include a switch array, switch matrix, multiplexer, and/or anyother type of switching device suitable to selectively couplestimulation energy to selected electrodes. The memory 439 can includeRAM, ROM, NVRAM, EEPROM or flash memory, but is not limited thereto.Various programs and/or stimulation parameter sets can be stored in thememory 439, examples of which are discussed herein.

Once a desired stimulation parameter set is determined, the IPG 102 canbe programmed with the optimal parameters of the set. The appropriateelectrode(s) 106 on the lead 104 then stimulate the nerve tissue withthe determined stimulation signal.

FIG. 14 is a simplified block diagram that illustrates possiblecomponents of an external programmer, such as a clinical programmer 200.Referring to FIG. 14, the clinical programmer 200 is shown as includinga power supply 440, a user interface 442, a controller 444, input andoutput (I/O) circuitry 446, telemetry circuitry 448 and memory 449.

The power supply 440, which can include a battery, can be used to powerthe various other components of the external programmer. As such, thepower supply 440 can be coupled to the user interface 442, thecontroller 444, the input and output (I/O) circuitry 446, the telemetrycircuitry 448 and the memory 449. A voltage regulator (not shown) canstep up or step down a voltage provided by a battery or an externalpower source to produce one or more predetermined voltages useful forpowering such components of the external programmer.

The clinician or other operator may utilize the clinical programmer 200to perform a variety of functions. For example, in some embodiments theclinical programmer 200 can be used to:

Turn OFF all stimulation.

Turn stimulation ON for up to four leads and measure lead impedance.

Assign body regions, electrode configurations and stimulation settingsfor each lead.

Enter patient and lead identification information, clinician and clinicname and contact information, and clinician's notes.

Perform a real time test to assess the patient stimulation response foreach lead.

Enable Patient Controlled Therapy and configure Patient ControlledTherapy settings for each lead.

Acquire identification, diagnostic, and historic information about theIPG 102.

Program configured therapy settings, and patient and clinicianinformation into the IPG 102 device.

The clinician may interact with the controller 444 via the userinterface 442 in order to test various stimulation parameter sets, inputuser feedback, select preferred or optimal programs, and the like. Theuser interface 442 can include a display, a keypad, a touch screen, oneor more peripheral pointing devices (e.g., a mouse, touchpad, joystick,trackball, etc.), and the like. The controller 444 can provide agraphical user interface (GUI) via the user interface 442 to facilitateinteraction with the clinician. The controller 444 can include amicroprocessor, a microcontroller, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field-programmablegate array (FPGA), a state machine, or similar discrete and/orintegrated logic circuitry. The I/O circuitry 446 can includetransceivers for wireless communication, ports for wired communicationand/or communication via removable electrical media, and/or appropriatedrives for communication via removable magnetic or optical media. Thetelemetry circuitry 448 can be the telemetry circuitry described above,or separate but similar telemetry circuitry.

FIG. 15A provides a perspective expanded view of an embodiment of aclinical programmer 200. In this embodiment, the clinical programmer 200comprises a handheld computer 202, such as a personal digital assistant,an antenna 204, a ground plane 206, and a telemetry controller 208 or“Base Station” (micro) plus RF board. As shown, the handheld computer202 includes a touch screen user interface 210 and an input and output(I/O) port 212. In this embodiment, these components are disposed withina housing comprising a cradle 214 and a faceplate 216, as shown.

Referring back to FIG. 14, the controller 444 can collect informationrelating to tested electrode parameters (e.g., combinations) andstimulation signal parameters, and store the information in the memory449 for later retrieval and review by a clinician or by the controller444 to facilitate identification of one or more preferred stimulationparameter sets. The controller 444 can send instructions to the IPG 102via the telemetry circuit 448 to cause the testing of variousstimulation parameter sets. For example, the controller 444 caneffectuate the testing of stimulation parameter sets created by thecontroller 444 or clinician to the IPG 102.

The memory 449 can include program instructions that, when executed bythe controller 444, cause the programmer 422 to perform at least some ofthe functions described herein. For example, the controller 444 canexecute program instructions that specify protocols for testing variousstimulation parameter sets and selecting one or more preferredstimulation parameter sets. The memory 449 can also store one or morestimulation parameter sets determined to treat a particular condition ofa patient, along with information about the patient. The memory 449 caninclude any volatile, non-volatile, fixed, removable, magnetic, optical,or electrical media, such as a RAM, ROM, CD-ROM, hard disk, removablemagnetic disk, memory cards or sticks, NVRAM, EEPROM, flash memory, andthe like.

In some embodiments, the clinical programmer 200 includes “workspaces”which are used to view and program the therapy settings and to obtaindiagnostic information. A record of the programmed settings anddiagnostic information is generated after every session. In someembodiments, four workspaces are provided: “Patient”, “Leads”, “Therapy”and “Stimulator”. FIG. 15B provides an example screenshot 250 of theclinical programmer 200. The four workspaces are shown as workspace tabs252 near the top of the screenshot 250.

In some embodiments, the Patient Workspace is used to: Enter patientidentification information; Enter IPG device information; Enterclinician, clinic name and contact information; and Enter clinician'snotes. In some embodiments, the Patient Workspace is divided into threetabs: “Patient Information”, “Clinician”, and “Notes”. Under the PatientInformation tab, information may be entered such as one or more of thefollowing: Patient Name, Date of Birth, Patient Address, Patient IDNumber, Stimulator Serial Number, Date of Implant, Lead Serial Numbers.Under the Clinician tab, information may be entered such as one or moreof the following: Physician Name, Clinic Name, Clinic Address, ClinicPhone Number, Clinic Email Address. Under the Notes tab, a text field isprovided to enter free text notes. Optionally, any previous informationthat has been entered in the text field will be erased when the textfield is updated.

In some embodiments, the Leads Workspace is used to: Activate (turn on)up to four leads; Adjust electrode configuration; Measure impedance; Setnominal values to begin stimulation; Perform trial mapping; Confirm andassign specific body regions to be stimulated. There is one Lead tab foreach lead, each Lead tab may be labeled with the corresponding bodyregion receiving stimulation. Each body region can have stimulationadjusted as described herein. FIG. 15B illustrates four body region tabs254, one each for right foot, left ankle, left foot, and lower back. Asmentioned, in some embodiments each lead has four electrodes. Each ofthe electrodes can be programmed with a positive or negative pulse, orbe programmed as neutral (off). For each lead, the pulse parameters arealso programmable. Typically, the pulse parameters include: PulseAmplitude (μA), Pulse Width (μs), Pulse Repetition Rate (Hz), andAllowed Impedance Range (Ω). The Allowed Impedance Range is dependent onvoltage and amplitude combinations. In some embodiments, each pulseparameter is selected from a drop-down table. The parameter choices arespecific to a variety of factors, including the anatomical target, andwill be described in later sections below.

Typically, each lead has a Maximum Allowable Charge. The calculatedvalue of the maximum allowable charge delivered by each lead may bedisplayed under its associated Lead tab. This value is calculated basedon the assigned pulse parameter settings and the lead's electrodeconfiguration. Thus, combinations of amplitude and pulse widthselections are typically limited by the maximum allowable charge.Therefore, for certain amplitude settings, only certain pulse widthsettings may be selectable. Similarly, for certain pulse width settings,only certain amplitude settings may be selectable.

In some embodiments, a Measure Impedance Button is included. The MeasureImpedance Button is activated to measure the lead's impedance. Onceactivated, the impedance value may be displayed.

In some embodiments, the clinical programmer 200 is used for TrialMapping. Trial Mapping allows the clinician to test and confirm patientstimulation response for each lead target or body region in real time.Typically, Trial Mapping starts with the use of signal parameters set torelatively low settings. Parameter settings are increased or decreasedby pressing the “Up” or “Down” arrow button respectively. FIG. 15Cillustrates an embodiment of a screenshot 260 showing a selectable stepsize buttons 262 when changing parameter settings. As will be describedin later sections, since the parameter values for the system 100 arelower than conventional stimulation systems, the granularity of controlor step size is also smaller. Thus, smaller increments are needed tocycle through the signal parameter values to determine the appropriatecombination of values to treat the condition. However, the clinician maydesire a variety of step sizes to narrow the range of parameter values.For example, the clinician may start with a larger step size (>>>) forgross changes in parameters values and then move to a smaller step size(>>) and even smaller step size (>) when approaching the desiredparameter value. Each enabled lead pulse parameter setting is adjusteduntil a desired response is achieved. The actual step sizescorresponding to the selectable step size buttons 262 are preprogrammedinto the programmer 200. It may be appreciated that as the clinicianscrolls through different ranges of the parameter values, the step sizewill automatically change to a granularity appropriate for the range.The settings are then saved to memory in preparation for programming ofthe IPG. The Trial Mapping process is then repeated for each activatedbody region.

In some embodiments, the Therapy workspace is used to: Enable or disablepatient controlled therapy for each lead; and Set maximum currentamplitude accessible for adjustment by the patient. Selecting “ON”enables Patient Controlled therapy. This allows the patient to adjusttherapy settings using their Patient Programmer. Selecting “OFF”disables and blocks patient access to Patient Controlled therapy. Whensetting Maximum Stimulation Amplitude Settings, the clinician typicallyenters the maximum stimulation amplitude from a clinically setamplitude, such as up to 4.0 mA, that the patient is allowed to set foreach lead.

In some embodiments, the Stimulator Workspace is used to: Acquireidentification, diagnostic, and historic information about the IPG:Program the IPG with therapy settings; and Program patient and clinicianinformation. In some embodiments, the Stimulator Workspace has two tabs,“Information” and “Program”. When the “Information” tab is selected, thescreen displayed is read only and may display one or more of thefollowing: Neurostimulator Serial Number (displays the serial number forthe IPG); NS Firmware Version (displays the Stimulator firmwareversion); Lead Serial Numbers (Displays each lead's serial number;Neurostimulator Clock Information (displays the time when the IPG wasfirst queried for that specific therapy session); and Implant Batteryinformation.

The “Program” tab is used to program the IPG with the configuredsettings including Leads settings and Patient Controlled therapysettings. In some embodiments, Patient and Stimulator IdentificationInformation is displayed under the “Program” tab. Such information mayinclude Patient Name; Patient Date of Birth; Stimulator Serial Number;and Stimulation Therapy Summary Table. The Stimulation Therapy SummaryTable, also referred to as “Stimulator Settings”, displays configuredstimulation therapy settings. In some embodiments, there are threecolumns: the first lists the parameter names; the second lists theretained values in the Clinical Programmer; the third lists theprogrammed values in the IPG. Optionally, stimulation therapy parametersmay be highlighted, such as using red text, to indicate parameters thathave been modified since the last stimulation therapy was programmed tothe IPG. Data may be presented in this order: Patient, Leads, andTherapy. Use of the vertical scroll bar may be used to display thedifferent parameters.

Additionally, in some embodiments, a “Program Stimulator” button isprovided under the “Program” tab. The “Program Stimulator” button isused to transfer the programmed values to the IPG. A table below the“Program Stimulator” button displays a summary of the configuredstimulation therapy settings. A confirmation window may be displayed toconfirm whether it is desired to program the IPG. Selecting a “Yes”button programs the settings displayed. Selecting a “No” button cancelsprogramming the IPG.

Typically, the patient programmer 300 that is to be used by the patientis specifically bound to the patient's IPG in order for the patient tobe able to minimally adjust the stimulation settings. Likewise, thepatient programmer 300 may be bound to multiple IPGs within a patient ifthe patient has been implanted with more than one IPG.

FIG. 16 is a simplified block diagram that illustrates possiblecomponents of an external programmer, such as a patient programmer 300.Referring to FIG. 16, the patient programmer 300 is shown as including apower supply 450, a user interface 452, a controller 454, input andoutput (I/O) circuitry 456, telemetry circuitry 458 and memory 459. Thepower supply 450, which can include a battery, can be used to power thevarious other components of the patient programmer 300. As such, thepower supply 450 can be coupled to the user interface 452, thecontroller 454, the input and output (I/O) circuitry 456, the telemetrycircuitry 458 and the memory 459. A voltage regulator (not shown) canstep up or step down a voltage provided by a battery or an externalpower source to produce one or more predetermined voltages useful forpowering such components of the patient programmer 300.

A patient can interact with the controller 454 via the user interface452 in order to select, modify or otherwise control delivery ofstimulation therapy. For example, the patient may be able to selectamong various stimulation parameter sets that are stored in the memory459. Additionally, or alternatively, the patient may be able to increaseor decrease specific stimulation signal parameters, such as amplitude,to tailor the therapy to the symptoms being experienced at the time. Theuser interface 442 can include a display, a keypad, a touch screen, oneor more peripheral pointing devices (e.g., a mouse, touchpad, joystick,trackball, etc.), and the like. The controller 454 can provide agraphical user interface (GUI) via the user interface 452 to facilitateinteraction with a patient. The controller 454 can include amicroprocessor, a microcontroller, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field-programmablegate array (FPGA), a state machine, or similar discrete and/orintegrated logic circuitry. The I/O circuitry 446 can includetransceivers for wireless communication, ports for wired communicationand/or communication via removable electrical media, and/or appropriatedrives for communication via removable magnetic or optical media.

In some embodiments, the memory 459 can store data related tostimulation parameter sets that are available to be selected by thepatient for delivery of stimulation therapy to the patient using the IPG102 implanted within the patient. In some embodiments, the controller454 can record usage information and store usage information in thememory 459. The memory 459 can include program instructions that, whenexecuted by the controller 454, cause the patient programmer 426 toperform functions ascribed to the patient programmer 300. The memory 459can include any volatile, non-volatile, fixed, removable, magnetic,optical, or electrical media, such as a RAM, ROM, CD-ROM, hard disk,removable magnetic disk, memory cards or sticks, NVRAM, EEPROM, flashmemory, and the like. Memory in IPG can record impedance data, current,voltage, time of day, time of therapy changes, built in circuit testing,battery data, to name a few. Upon connection with an externalprogrammer, the programmer can record the IPG recorded data. This datacan then be used to reprogram the IPG.

The telemetry circuitry 458 allows the controller to communicate withIPG 102, and the input/output circuitry 456 may allow the controller 454to communicate with the clinician external programmer 200. Thecontroller 454 can receive selections of, or adjustments to, stimulationparameter sets made by the patient via the user interface 452, and cantransmit the selection or adjustment to the IPG 102 via telemetrycircuitry 458. Where the patient programmer 300 stores data relating tostimulation parameter sets in the memory 459, the controller 454 canreceive such data from the clinician programmer 200 via the input/outputcircuitry 456 during programming by a clinician or physician. Further,the patient programmer 300 can transmit data relating to stimulationparameter sets to the IPG 102 via the telemetry circuitry 458.

The patient may utilize the patient programmer 300 to perform a varietyof functions. For example, in some embodiments the patient programmer300 can be used to:

Turn OFF all stimulation, if desired.

Turn stimulation ON or OFF for each body region to be stimulated.

Adjust the amount of stimulation for each body region.

View the IPG identification information including the stimulator serialnumber, each lead's serial number, and the date when the IPG was lastprogrammed.

View the patient's name (optionally, the study ID number).

View the lead placement date.

View the clinician name, clinic name and contact information.

Typically, the patient programmer 300 includes a Main Menu whichdisplays two main functions: Adjust Stimulation Settings and ProgrammerSetup. The Adjust Stimulation Settings allows the user to set upcommunication with the IPG and adjust stimulation settings. TheProgrammer Setup allows the patient to set the Patient Programmer dateand time, and to view information about the IPG and Patient Programmercontrols. Often the Main Menu has some basic information identifying thedevice. In addition, the physician, clinic and the clinic phone numberare typically displayed, along with the Programmer Serial Number,Software Version and Base Station Firmware Version. Further, the MainMenu may include the IPG connection status, the battery charge level andthe time.

In some embodiments, the patient can cause the IPG to check forcommunication from the patient programmer 300 with the use of a magnetwithin or associated with the patient programmer 300. The patient mayplace the magnet near the IPG, such as within 6 feet, for a period oftime, such as 5 seconds or more.

When four leads are implanted and programmed by the clinician for use,the patient can turn stimulation therapy ON or OFF for up to four areasof the body and adjust the amount of stimulation any of those areas arereceiving as allowed by the clinical programmer. It may be appreciatedthat such functionality applies to any number of leads which areimplanted and programmed for use. To turn stimulation therapy ON or OFF,the Patient Programmer 300 may display the names of one to fourdesignated body regions that the leads have been placed to stimulate andthe patient individually turns stimulation of each region on or off.

In some embodiments, when stimulation is ON, the patient may adjust theamount of stimulation to the body region. For example, once the correcttab has been selected for the specific body region to be adjusted, thepatient may press the “Down” button to decrease the stimulation level orpress the “Up” button to increase the stimulation level. In someembodiments, a stimulation level indicator between the “Up” and “Down”buttons moves up or down as the patient changes the stimulation levelfor the selected body region. Further, the stimulation level indicatormay also show the current stimulation level and where it is compared tothe maximum set by the clinician. The adjustments may then be saved andthe patient can continue to adjust stimulation to other specific bodyregions.

The above described implantable stimulation system 100 can be used tostimulate a variety of anatomical locations within a patient's body. Inpreferred embodiments, the system 100 is used to stimulate one or moredorsal roots, particularly one or more dorsal root ganglions. FIG. 17illustrates example placement of the leads 104 of the embodiment of FIG.7 within the patient anatomy. In this example, each lead 104 isindividually advanced within the spinal column S in an antegradedirection. Each lead 104 has a distal end which is guidable toward atarget DRG and positionable so that its electrodes 106 are in proximityto the target DRG. Specifically, each lead 104 is positionable so thatits electrodes 106 are able to selectively stimulate the DRG, either dueto position, electrode configuration, electrode shape, electric fieldshape, stimulation signal parameters or a combination of these as willbe discussed in more detail in a later section. FIG. 17 illustrates thestimulation of four DRGs, each DRG stimulated by one lead 104. Thesefour DRGs are located on three levels, wherein two DRGs are stimulatedon the same level. It may be appreciated that number of DRGs and anycombination of DRGs may be stimulated with the stimulation system 100 ofthe present invention. It may also be appreciated that more than onelead 104 may be positioned so as to stimulate an individual DRG and onelead 104 may be positioned so as to stimulate more than one DRG.

FIG. 18 illustrates an example cross-sectional view of an individualspinal level showing a lead 104 of the stimulation system 100 positionedon, near or about a target DRG. The lead 104 is advanced along thespinal cord S to the appropriate spinal level wherein the lead 104 isadvanced laterally toward the target DRG. In some instances, the lead104 is advanced through or partially through a foramen. At least one,some or all of the electrodes 106 are positioned on, about or inproximity to the DRG. In preferred embodiments, the lead 104 ispositioned so that the electrodes 106 are disposed along a surface ofthe DRG opposite to the ventral root VR, as illustrated in FIG. 18. Itmay be appreciated that the surface of the DRG opposite the ventral rootVR may be diametrically opposed to portions of the ventral root VR butis not so limited. Such a surface may reside along a variety of areas ofthe DRG which are separated from the ventral root VR by a distance.

In some instances, such electrodes 106 may provide a stimulation regionindicated by dashed line 110, wherein the DRG receives stimulationenergy within the stimulation region and the ventral root VR does not asit is outside of the stimulation region. Thus, such placement of thelead 104 may assist in reducing any possible stimulation of the ventralroot VR due to distance. However, it may be appreciated that theelectrodes 106 may be positioned in a variety of locations in relationto the DRG and may selectively stimulate the DRG due to factors otherthan or in addition to distance, such as due to stimulation profileshape and stimulation signal parameters, to name a few. It may also beappreciated that the target DRG may be approached by other methods, suchas a retrograde epidural approach. Likewise, the DRG may be approachedfrom outside of the spinal column wherein the lead 104 is advanced froma peripheral direction toward the spinal column, optionally passesthrough or partially through a foramen and is implanted so that at leastsome of the electrodes 106 are positioned on, about or in proximity tothe DRG.

In order to position the lead 104 in such close proximity to the DRG,the lead 104 is appropriately sized and configured to maneuver throughthe anatomy. Such maneuvering includes atraumatic epidural advancementalong the spinal cord S, through a sharp curve toward a DRG, andoptionally through a foramen wherein the distal end of the lead 104 isconfigured to then reside in close proximity to a small target such asthe DRG. Consequently, the lead 104 is significantly smaller and moreeasily maneuverable than conventional spinal cord stimulator leads.Example leads and delivery systems for delivering the leads to a targetsuch as the DRG are provided in U.S. Provisional Patent Application No.61/144,690, filed Jan. 14, 2009 entitled “STIMULATION LEAD, DELIVERYSYSTEM AND METHODS OF USE” by Fred I. Linker et al. and is incorporatedherein by reference for all purposes.

In addition, by positioning the electrodes 106 in dose proximity to thetarget tissue, less energy is required for stimulation. This reductionin energy allows a reduction in electrode size, among other benefits. Insome embodiments, the average electrode surface area is approximately1-6 mm², particularly approximately 2-4 mm², more particularly 3.93 mm²whereas conventional spinal cord stimulators typically have a muchlarger average electrode surface area, such as T5 mm² for some leads or12.7 mm² for traditional paddle leads. Likewise, in some embodiments anaverage electrode length is 1.25 mm whereas conventional spinal cordstimulators typically have an average electrode length of 3 mm. Suchreduced electrode sizing allows more intimate positioning of theelectrodes in the vicinity of the DRG and allows for IPGs havingdifferent control and performance parameters for providing direct andselective stimulation of a targeted neural tissue, particularly the DRG.In addition, in some embodiments, the overall dimensions of one or moreelectrodes and the spacing of the electrodes is selected to match ornearly match the overall dimensions or size of the stimulation target.In an embodiment where the targeted neural tissue is a substantialportion of a dorsal root ganglion, the electrode or electrodes arrayedalong the lead are sized and spaced so that a majority of the electrodeslie along the overall dimensions of the dorsal root ganglion. Forexample, if there are 4 electrodes on a lead to stimulate a dorsal rootganglion having a length of about 8 mm, then the overall length of theelectrode portion of the lead should be between about 6-10 mm. FIG. 18illustrates one example where all 4 of the electrodes on the lead arewithin the lateral dimension of the DRG as shown. The size and spacingof the electrodes may align with other DRG dimensions as well. In onespecific aspect, the spacing of the electrodes is such that when placednear the targeted dorsal root ganglion two or more electrodes are inposition to provide therapeutic energy to the targeted dorsal rootganglion. Since the size of the ganglion depends on the spinal level andother factors, a variety of different electrode sizes and spacing may beused to tailor the electrode portion to selected dorsal root ganglia. Itmay also be appreciated that in some embodiments, the electrodes 106 aredirectional so as to provide direct and selective stimulation andfurther decrease energy required for stimulation.

In some embodiments, the electrodes 106 are spaced 5 mm apart along thedistal end of the lead 104. In other embodiments, the electrodes 106 arespaced 0.250 inches apart, from center to center, and 0.200 inchesapart, from inside edge to inside edge. In most patients, the DRG has asize of 5-10 mm. Therefore, typical spacing would allow two electrodes106 to be in contact with the target DRG while the remaining twoelectrodes are in the vicinity of the target DRG. In some instances, thetwo electrodes 106 in contact with the DRG are used to stimulate the DRGwhile the remaining two electrodes 106 do not provide stimulationenergy. In other instances, all four electrodes 106 provide stimulationenergy to the DRG, two electrodes providing energy to the DRG at adistance somewhat closer to the DRG than the other two electrodes. Itmay be appreciated that any combination of electrodes 106 may providestimulation energy and each electrode 106 may provide a different levelor type of stimulation signal. Consequently, a variety of electric fieldshapes may be generated, each shape potentially causing a differenttreatment effect. In many embodiments, the electric field shape will beelliptical. Likewise, the position of the electric field in relation tothe anatomy may also be adjusted to potentially cause differenttreatment effects. Such effects will be described in greater detailbelow. It may also be appreciated that the electrodes 106 providingstimulation energy may change over time. For example, if a lead 104 hasmigrated, a different combination of electrodes 106 may be used tostimulate the target DRG in the new lead position.

As mentioned above, the intimate positioning of the leads 104 of thepresent invention allows the stimulation system 100 to have a variety ofadditional beneficial features. For example, positioning the leads 104in such close proximity to the target tissue allows for smallerstimulation regions. This in turn allows for smaller electrode surfaceareas and reduced energy requirements. A reduction in energyrequirements allows for smaller battery size, increased batterylongevity and the possibility of the elimination of battery replacementor recharging altogether. Typically, patients with conventional systemseither have an IPG with a standard battery wherein the IPG is surgicallyreplaced when the battery wears out or they have an IPG with arechargeable battery wherein the battery is recharged by an externaldevice worn for a few hours every two or three weeks. In contrast, thesystem 100 of the present invention draws such low energy that thebattery longevity is sufficient for the life of the device. Thus, thepatient will not need to undergo additional surgeries to replace thebattery, therefore reducing any risks of surgical complications. Thepatient will also not need to recharge the battery which increasesquality of life and provides for more continuous therapy. In both cases,less clinical follow-up may be necessary which reduces costs andincreases patient satisfaction. However, it may be appreciated thatrechargeable batteries may be used.

The energy requirement for the stimulation system 100 of the presentinvention is exceptionally low, particularly in comparison toconventional spinal cord stimulation systems. Energy is the work done inmoving an electric charge (q) between two points with a potentialdifference (v) between them. Recall that if (q) is the electric charge,which varies with time (t), then the resulting current is given byi=dq/dt. The unit of current is the ampere. Power is the rate in whichwork is done. Consider a charge (dq) moving from point A to point Bin atime interval (dt) and let the potential difference between A and B be(v). Then the work done on the charge (dq) is

dw=vdq=v(idt)

-   Then the power is given by

p=dw/dt=vi

-   The unit of power is the watt. One watt equals 1 joule/second. As    mentioned, energy is the work done in moving an electric charge (q)    between two points with a potential difference between them. Since    power equals the derivative of energy, energy equals the integral of    power. The energy delivered or received by a component at time (t)    is therefore given by

w(t)=∫p(t)dt

-   The unit of energy is joules. The movement of electric charge (q)    between these two points depends on the resistance R.

R=v(t)/i(t)

-   A unit of resistance is the ohm (Ω). Therefore, one ohm equals 1    volt/amp. And, therefore:

p(t)=R[/(t)]²

-   Thus, energy delivered or received by a component at a time (t) is    also related to resistance.

To determine the differences in energy requirement between thestimulation system 100 of the present invention and conventional spinalcord stimulation systems, the respective stimulation signals can becompared. In one embodiment, the stimulation signal of the presentinvention has a rectangular waveform, such as illustrated by a trace 120shown in FIG. 19A, wherein the pulse width is approximately 80 μs andthe current amplitude is approximately 200 μA. The integral of thiscurve (i.e. the area under this curve) is the total charge,corresponding to the energy and related to tissue impedance. In thisexample, the charge delivered is (200 μA)×(80 μs)=16 nC per pulse. FIG.19B illustrates an embodiment of a trace 122 showing the voltageresponse to a complex impedance stimulating biological tissue. Thus, thetotal energy used is 7 nJ, wherein the Warburg resistance is 650Ω, theWarburg capacitance is 0.2 μF and the tissue resistance is 1000Ω.

FIG. 20A illustrates a trace 124 representing an example stimulationsignal of a conventional spinal cord stimulator. Here the pulse width isapproximately 200 μs and the current amplitude is approximately 1.7 mA(or 1700 μA) which is around an order of magnitude greater than thecurrent amplitude of the stimulation system 100 of the presentinvention. Thus, the charge delivered is (200 μs)×(1.7 mA)=340 nC. FIG.20B illustrates an embodiment of a trace 126 representing the voltageresponse to a complex impedance stimulating biological tissue. Thus, thetotal energy used is 1294 nJ, wherein the Warburg resistance is 200Ω,the Warburg capacitance is 0.5 μF and the tissue resistance is 1000Ω. Inthis example, the energy supplied by the stimulation system 100 of thepresent invention is 0.54% (7 nJ/1294 nJ) of the energy supplied byconventional stimulation systems. This significant reduction in energyis due to the lower energy requirements of selectively stimulating thetarget anatomy, particularly the DRG. Typically, the energy supplied bythe stimulation system 100 of the present invention is less than 10% ofconventional systems, particularly less than 5%, more particularly lessthan 1%.

It may be appreciated that the above example is for illustrativepurposes. FIG. 21 illustrates additional data indicating the stimulationsignal parameters which selectively targeted the DRG. As shown, there isan energy threshold in which the DRG is stimulated which is below theenergy threshold in which the ventral root is stimulated. By providingstimulation signals below the ventral root threshold, the patient's painsensations may be blocked without the negative side effects of ventralroot stimulation.

Due to variability in patient anatomy, pain profiles, pain perceptionand lead placement, to name a few, signal parameter settings will likelyvary from patient to patient and from lead to lead within the samepatient. Signal parameters include voltage, current amplitude, pulsewidth and repetition rate, to name a few. In some embodiments of thestimulation system 100 of the present invention, the voltage provided isin the range of approximately 0-7 volts. In some embodiments, thecurrent amplitude provided is less than approximately 4 mA, particularlyin the range of approximately 0.5-2 mA, more particularly in the rangeof approximately 0.5-1.0 mA, 0.1-1.0 mA, or 0.01-1.0 mA. Further, insome embodiments, the pulse width provided is less than approximately2000 μs, particularly less than approximately 1000 μs, more particularlyless than approximately 500 μs, or more particularly 10-120 μs. And, insome embodiments, the repetition rate is in the range of approximately2-120 Hz, up to 200 Hz or up to 1000 Hz.

Typically, stimulation parameters are adjusted until satisfactoryclinical results are reached. Thus, there is an envelope of stimulationparameter value combinations between the threshold for DRG stimulationand ventral root stimulation for any given lead positioned in proximityto any given DRG per patient. The specific combinations or possiblecombinations that could be used to successfully treat the patient aretypically determined perioperatively in vivo and postoperatively ex vivoand depend on a variety of factors. One factor is lead placement. Thecloser the desired electrodes are to the DRG the lower the energyrequired to stimulate the DRG. Other factors include electrodeselection, the anatomy of the patient, the pain profiles that are beingtreated and the psychological perception of pain by the patient, to namea few. Over time, the parameter values for any given lead to treat thepatient may change due to changes in lead placement, changes inimpedance or other physical or psychological changes. In any case, theenvelope of parameter values is exceedingly lower than those ofconventional stimulation systems which require energy delivery of atleast an order of magnitude higher to treat the patient's paincondition.

Given the lower ranges of parameter values for the system 100 of thepresent invention, the granularity of control is also smaller incomparison to conventional stimulation systems. For example, current ina conventional stimulation system is typically adjustable in incrementsof 0.1 mA. In some embodiments of the present invention, this incrementis larger than the entire range of current amplitude values that may beused to treat the patient. Thus, smaller increments are needed to cyclethrough the signal parameter values to determine the appropriatecombination of values to treat the condition. In some embodiments, thesystem 100 of the present invention provides control of currentamplitude at a resolution of approximately 25 μA, particularly whenusing a current amplitude under, for example, 2 mA, however it may beappreciated that smaller increments may be used such as approximately 10μA, 5 μA or 1 μA. In other embodiments, control of current amplitude isprovided at a resolution of approximately 50 μA, particularly when usinga current amplitude of, for example, 2 mA or greater. It may beappreciated that such a change in resolution may occur at other levels,such as 1 mA. Similarly, voltage in a conventional stimulation system istypically adjustable in increments of 100 mV. In contrast, someembodiments of the present invention provide control of voltage at aresolution of 50 mV. Likewise, some embodiments of the present inventionprovide control of pulse width at a resolution of 10 μs. Thus, it may beappreciated that the present invention provides a high granularity ofcontrol of stimulation parameters due to the low ranges of parametervalues.

It may be appreciated that in some instances even lower levels of energymay be used to successfully treat a patient using the stimulation system100 of the present invention. The closer a lead is positioned to atarget DRG, the lower the level of energy that may be needed toselectively stimulate the target DRG. Thus, signal parameter values maybe lower than those stated herein with correspondingly highergranularity of control.

Utilizing these signal parameter values, the stimulation profile iscustomized for the patient and programmed into the memory 108 of the IPG102. As mentioned above, the IPG 102 is typically programmed through acomputerized programming station or programming system. This programmingsystem is typically a self-contained hardware/software system, or can bedefined predominately by software running on a standard personalcomputer (PC). The PC or custom hardware can have a transmitting coilattachment or antenna to allow for the programming of implants, or otherattachments to program external units. Patients are generally providedhand-held programmers (patient programmer 300) that are more limited inscope than are the physician-programming systems (clinical programmer200), with such hand-held programmers still providing the patient withsome control over selected parameters. Thus, this allows for easychanges to the stimulation profile over time, as needed.

As mentioned previously, effective treatment of a condition may beachieved by directly stimulating a target anatomy associated with thecondition while minimizing or excluding undesired stimulation of otheranatomies. When such a condition is limited to or primarily affects asingle dermatome, the present invention allows for stimulation of asingle dermatome or regions within a dermatome (also referred to assubdermatomal stimulation). A dermatome is considered the body regionthat is innervated by a single spinal level. FIG. 22 illustrates thedermatomal arrangement or “map” of dermatomes along a patient P. Thedermatomes form into bands around the trunk but in the limbs theirorganization is more complex as a result of the dermatomes being “pulledout” as the limb buds form and develop into the limbs duringembryological development. Each dermatome is labeled according to itsassociated spinal level. Upper bodily regions are innervated by nervestraveling in the cervical spinal segments and as the innervation patternprogresses caudally so do the spinal segments innervating the dermatome.Thus, regions in the middle of the body (thorax, etc) are innervated bythoracic spinal segments and lower bodily regions are innervated bylumbar and sacral spinal segments.

The nerves innervating a dermatome originate from DRGs on the associatedspinal level Since each dermatome is supplied by a single pair of DRGs,stimulation of one or both of these DRGs will substantially effect asingle dermatome. Referring back to FIG. 17, the present inventionprovides for stimulation of a single DRG or a pair of DRGs on a singlespinal level independently of other DRGs or nerve tissues in thesurrounding area. This allows for a single dermatome to be stimulated.It may be appreciated that there is overlap of innervation betweenadjacent dermatomes. However, stimulation of one or more DRGs on aspinal level will largely affect the directly associated dermatome withsignificantly lesser affects in adjacent dermatomes. Likewise,stimulation of a single DRG on, for example, the right side of thespinal column will largely affect the right side of the body within thedirectly associated dermatome. Thus, stimulation of a single DRG maystimulate a portion of a single dermatome. This is not the case withconventional spinal stimulation systems which simultaneously stimulatemultiple dermatomes. By design, such conventional systems cannot isolatea single dermatome or a portion of a dermatome for treatment and suchstimulation will substantially affect more than one dermatome.

FIG. 23 schematically illustrates DRGs on various spinal levels withassociated body regions that may be affected by selective stimulation ofthe individual DRGs. For example, stimulation of DRG1 on the right sideof L5 may affect the foot, lower leg and/or low back on the right sideof the patient. Likewise, stimulation of DRG2 on the right side of L4may affect the leg and/or low back on the right side of the patient.FIGS. 24A 4B illustrate these body regions along the dermatomes of thepatient P. FIG. 24A illustrates the patient P from the back, includingthe dermatomes of the lower body and a schematic representation of thegeneral area of the DRGs. The region of the L5 dermatome that is likelyaffected by stimulation of DRG1 is indicated by double-hatched lines.Likewise, FIG. 24B illustrates the patient P from the front, includingthe dermatomes of the lower body. Again, the region of the L5 dermatomethat is likely affected by stimulation of DRG1 is indicated bydouble-hatched lines. This portion of the dermatome extends along thebottom of the right foot, the top of the right foot, along the lower legand up to the low back. Similarly, the region of the L4 dermatome thatis likely affected by stimulation of DRG2 is indicated by hatched linesin both FIG. 24A and FIG. 24B. This portion of the dermatome mainlyextends along the front of the lower leg and up to the low back. Thus,for patients having pain or another condition in these body regions,DRG1 and DRG2 may be stimulated so as to treat such conditions whileminimally or not affecting other body regions.

Referring back to FIG. 23, traditional placement of a conventionalspinal stimulation system (such as illustrated in FIG. 5) is alsoillustrated wherein the lead 14 is positioned along the midline of thespinal column S so that the electrodes 20 are aligned with the saggittaland parasaggittal midline. Such placement causes the electrodes 20 tostimulate many neural fibers innervating body regions unassociated andunaffected by the condition for which treatment is desired. In thisexample, stimulation by the electrodes 20 would affect the T12, L1, L2,L3, L4, L5 dermatomes on both sides of the patient's body.

FIG. 25 schematically illustrates selective stimulation of DRG1according to aspects of the present invention. As shown, a lead 104 ispositioned so that at least one of the at least one electrode 106 ispositioned on, near or about the target DRG (DRG1). Different bodyregions associated with DRG1 (foot, lower leg, low back) may be tracedto specific sensory neurons within the DRG1. In particular, each sensoryneuron includes a cell body or soma which may be targeted to stimulatethe sensory neuron independently of other surrounding neurons. In thisexample, the lower leg is associated with soma N1, the low back isassociated with soma N2, and the foot is associated with soma N3. It hasbeen suggested by a variety of scientific studies that there is aspecific somatotopic orientation of neurons (and associated somas)within the DRG subserving sensory function to distinct anatomy.

A somatotopic map is an anatomically specific orientation of sensoryintegration. It is well-known that once sensory information has traveledinto the central nervous system, a “somatotopic” map is organized in thecortex of the brain. Thus, specific regions of the somatosensory cortexare involved in sensory processing from specific anatomical regions.Thus, stimulation of various regions of specific sub-regions of thesomatosensory cortex will result in the perception of sensory input fromspecific anatomical regions. In addition, research has suggested thatnot only are there somatotopic maps within the central nervous system,but also in spinal neural structures such as the dorsal root ganglion.Typically, such mapping has been completed in animal studies byinjecting tracer chemicals in peripheral anatomical structures and thenlooking at labeled cells in the DRG to see the relative distribution ofthose labeled cells. The dorsal root ganglion is a special neuralstructure that contains the cell bodies (soma) of the neurons that areinnervating specific dermatomes. The understanding of a somatotopic mapfor the dorsal root ganglion may allow for the targeting of portions ofthe DRG to provide therapy to one or more specific regions within thedermatome associated with that DRG. Thus, subdermatomal targeting mayallow very specific therapeutic application in the treatment of pain andother conditions.

Referring again to FIG. 25, portions of the DRG may be selectivelystimulated to affect specific regions within a dermatome. In thisembodiment, soma N1, soma N2, or soma N3 may be stimulated to causedifferent treatment effects. Likewise, two or more of the somas N1, N2,N3 may be stimulated in combination to cause further treatment effects.Each soma may be selectively stimulated by manipulation of one or moreof the following features: position of the electrode(s) 106 in relationto the DRG, selection of the electrode combinations for stimulation, andprogramming of the stimulation signal parameters, such as pulse width,amplitude, and frequency. By such manipulation, a desired electricalfield is generated and positioned relative to the DRG to stimulate aparticular portion of the DRG in three-dimensional space. Thisparticular portion typically includes the one or more somas which aretargeted to influence the desired treatment effect.

FIGS. 26A-26D illustrate perspective views of a lead 104 stimulating aportion of DRG1 to affect a specific region within a dermatome.Referring to FIG. 26A, DRG1 is shown to include soma N1, soma N2, andsoma N3. The lead 104 is positioned on, near or about the DRG1 accordingto the methods of the present invention. In this example, two electrodes106 a, 106 b are selected for stimulation while the remaining twoelectrodes 106 c, 106 d are neutral. An electric field 500 is generatedby the two electrodes 106 a, 106 b according to chosen stimulationsignal parameters so as to stimulate soma N3 while providing minimal orno stimulation to soma N1 and soma N2. In this embodiment, soma N3 isassociated with the body region of the foot whereas soma N1 isassociated with the low back and soma N2 is associated with the lowerleg. Thus, the patient will have a targeted treatment effect in the footwithout a treatment effect in the low back and lower leg within the samedermatome. FIG. 26B rotates the view of FIG. 26A to illustrate thethree-dimensional electric field 500 and its inclusion of soma N3 alongwith exclusion of soma N1 and soma N2. Likewise, FIG. 26C rotates theview of FIG. 26A to provide a perspective end view, wherein again thethree-dimensional electric field 500 is shown to include soma N3 whileexcluding soma N1 and soma N2. And further, FIG. 25D rotates the view ofFIG. 25A to provide a perspective bottom view of the lead 104 inproximity to the DRG1 so that the electric field 500 stimulates soma N3while excluding soma N1 and soma N2.

Different somas may be selectively stimulated by physically moving thelead 104 in relation to the DRG1. For example, by moving the lead 104along the surface of the DRG1, the electric field 500 can be moved toselect different somas, such as soma N1 while excluding somas N2, N3.Or, the lead 104 can remain stationary in relation to the DRG1, anddifferent electrodes 106 may be utilized for stimulation to move theelectric field 500. Likewise, the shape of the electric field 500 can bechanged by changing the electrode combination and/or changing thestimulation signal parameters. For example, the electric field 500 maybe increased in size by changing stimulation signal parameters, such asincreasing the amplitude. Or, the size of the electric field 500 may beincreased by changing the electrode combination, such as by utilizing anadditional electrode for stimulation. In this example, the size of theelectric field 500 may be increased to include both soma N3 and soma N1,while substantially excluding soma N2. This would cause the patient tohave a targeted treatment effect in the foot and low back without atreatment effect in the lower leg within the same dermatome. Similarly,the size of the electric field 500 may be increased to include somas N1,N2, N3. This would cause the patient to have a targeted treatment effectin the foot, low back and lower leg within the same dermatome.

FIGS. 27-28 provide clinical data which illustrate the correlationbetween changes in electrode combination and/or signal parameters andthe resultant changes in affected body region. The clinical data wasgathered during a clinical trial in which the patient subjects wereimplanted with one or more leads 104 in accordance with the presentinvention. Each lead 104 was positioned so that at least one of its oneor more electrodes 106 was on, near or about a DRG, such as illustratedin FIGS. 17-18.

FIG. 27 provides a table of clinical data from Patient No. 1, whereinone lead (Lead No. 2) was implanted so as to stimulate a DRG on levelL5. As shown in Row 1 of the table, each electrode or contact along thelead is labeled by number (1, 2, 3, 4) wherein there were fourelectrodes present. Contact 1 and Contact 2 were configured as Off orNeutral (N). And, Contact 3 was configured as an anode (+) while Contact4 was configured as a cathode (−). The signal parameters were set asfollows: amplitude=800 μA, pulse width=60 μs, frequency=70 Hz. It may beappreciated that this clinical data was gathered in an effort to mapbody regions affected by stimulation of portions of the associated DRG.Therefore, the parameter settings were not necessarily within thedesired ranges for treatment. At these signal parameter settings, thebottom of the patient's foot was affected by the stimulation. As shownin Row 2 of the table, the amplitude was raised to 1.8 mA while allother variables remained the same. Consequently, both the patient's footand calf were affected by the stimulation. Thus, the electric fieldprovided by Contact 3 and Contact 4 was enlarged causing additionalsensory neurons to be stimulated. Further, Row 3 of the table shows thatwhen the amplitude was raised to 2.25 mA, the affected body region wasexpanded to include the back of the knee. Likewise, Row 4 of the tableshows that when the amplitude was raised to 2.75 mA, the affected bodyregion was expanded to include the hip and Row 5 of the table shows thatwhen the amplitude was raised to 3.0 mA, the affected body region wasexpanded to include the buttock. Thus, as the electric field provided byContact 3 and Contact 4 changed shape, additional sensory neurons werestimulated causing additional body regions of the dermatome to beaffected. This illustrates that subdermatomal stimulation may beachieved by manipulating the electric field and signal parameters.

FIG, 28 provides a table of clinical data from a different patient,Patient No. 2, wherein one lead (Lead No. 1) was implanted so as tostimulate a DRG on level L4. As shown in Row 1 of the table, eachelectrode or contact along the lead is labeled by number (1, 2, 3, 4)wherein there were four electrodes present. Contact 1 and Contact 2 wereconfigured as Off or Neutral (N). And, Contact 3 was configured as ananode (+) while Contact 4 was configured as a cathode (−). The signalparameters were set as follows: amplitude=325 μA, pulse width=120 μs,frequency=60 Hz. Again, it may be appreciated that this clinical datawas gathered in an effort to map body regions affected by stimulation ofportions of the associated DRG. Therefore, the parameter settings werenot necessarily within the desired ranges for treatment. At these signalparameter settings, the patient's calf was affected by the stimulation.As shown in Row 2 of the table, the amplitude was raised to 350 μA whileall other variables remained the same. Consequently, both the patient'scalf and knee were affected by the stimulation. Thus, the electric fieldprovided by Contact 3 and Contact 4 was enlarged causing additionalsensory neurons to be stimulated. Further, Row 3 of the table shows thatwhen the amplitude was raised to 425 μA, the affected body region wasexpanded to include the hip. Thus, as the electric field provided byContact 3 and Contact 4 was enlarged, additional sensory neurons werestimulated causing additional body regions of the dermatome to beaffected.

Row 4 of the table of FIG. 28 shows a change in the electrodeconfiguration. Here, Contact 1 remained Off or Neutral (N) while Contact2 was configured as a cathode (−). Contact 3 was configured as an anode(+) and Contact 4 was configured as a cathode (−). The signal parameterswere set as follows: amplitude=275 μA, pulse width=120 μs, frequency=60Hz. Consequently, at these signal parameter settings, the patient's calfto ankle was affected by the stimulation. Thus, in comparison to Row 1,although the amplitude was lowered, the altered shape of the electricfield provided by the new electrode configuration allowed for additionalsensory neurons to be stimulated.

A comparison of Row 5 and Row 6 illustrate the effect of changingelectrode configuration while other variables remain the same. As shownin Row 5 of the table, Contact 1 was Off or Neutral (N) while Contact 2was configured as a cathode (−), Contact 3 was configured as an anode(+) and Contact 4 was configured as a cathode (−). The signal parameterswere set as follows: amplitude=625 μA, pulse width=120 μs, frequency=60Hz. At these signal parameter settings, affected body regions were abovethe knee and to the side of the thigh. While keeping the same signalparameter settings, the electrode configuration was changed so thatContact 1 was Off or Neutral (N) while Contact 2 was configured as ananode (+), Contact 3 was configured as an cathode (−) and Contact 4 wasconfigured as an anode (+), as shown in Row 6 of the table. This changein the electric field caused the affected body region to change to thefront of the calf. Raising the amplitude, as shown in Row 7, increasedthe affected body region to include the knee. Row 8 shows a change inboth amplitude and pulse width, which creates a different affect withinthe dermatome. And, again, raising the amplitude, as shown in Row 9,increases the affected body region. This further illustrates thatsubdermatomal stimulation may be achieved by manipulating the electricfield and signal parameters to affect particular body regions whileleaving other body regions substantially unaffected.

It may be appreciated that in some embodiments subdermatomal stimulationis achieved by factors other than or in addition to somatotopic mappingof the DRG. In these embodiments, body regions that are considered asfocal areas of the condition for which the patient is being treated werepreferentially affected by the stimulation. For example, when thecondition being treated is pain, body regions that the patientconsidered to be painful are preferentially affected by the stimulation.This suggests that DRG stimulation therapy preferentially neuromodulatesneural elements that are involved in the pain condition specific to thearea of pain. This corroborates with basic neurophysiologic data thatsuggest both small diameter soma and large diameter neurons residing inthe DRG involved in the neural transduction of pain and othersomatosensory signals undergo physiologic changes that affect thebiophysics of the cell membrane. This suggests that neurons becomehyperexcitable possibly through the altered function of transmembraneintegral membrane proteins—in particular ion channels. This alteredbiophysical function of the cells involved in the processing of paininformation would provide a basis for enhanced ability to neuromodulatethe cell function with electrical fields. This, in turn, would underliethe ability to preferentially generate pain relief and paresthesias inthe selected anatomically painful regions.

A variety of pain-related conditions are treatable with the systems,methods and devices of the present invention. In particular, thefollowing conditions may be treated: 1) Failed Back Surgery syndrome; 2)Chronic Intractable Low Back Pain due to: A) Unknown Etiology, B) Lumbarfacet disease as evidenced by diagnostic block(s), C) Sacroiliac Jointdisease as evidenced by diagnostic block(s), D) Spinal Stenosis, E)Nerve root impingement—non-surgical candidates, F) DiscogenicPain—discography based or not; 4) Complex Regional Pain Syndrome; 5)Post-Herpetic Neuralgia; 6) Diabetic Neuropathic Pain; 7) IntractablePainful Peripheral Vascular Disease; 8) Raynaud's Phenomenon; 9) PhantomLimb Pain; 10) Generalized Differentiation Pain Conditions; 11) Chronic,Intractable Angina; 12) Cervicogenic Headache; 13) Various VisceralPains (pancreatitis, etc.); 14) Post-Mastectomy Pain; 15) Vuvlodynia;16) Orchodynia; 17) Painful Autoimmune Disorders; 18) Post-Stroke Painwith limited painful distribution; 19) Repeated, localized sickle cellcrisis; 20) Lumbar Radiculopathy; 21) Thoracic Radiculopathy; 22)Cervical Radiculopathy; 23) Cervical axial neck pain, “whiplash”; 24)Multiple Sclerosis with limited pain distribution Each of the abovelisted conditions is typically associated with one or more DRGs whereinstimulation of the associated DRGs provides treatment or management ofthe condition.

Likewise, the following non-painful indications or conditions are alsotreatable with the systems, methods and devices of the presentinvention: 1) Parkinson's Disease; 2) Multiple Sclerosis; 3)Demylenating Movement Disorders; 4) Physical and Occupational TherapyAssisted Neurostimulation; 5) Spinal Cord Injury—NeuroregenerationAssisted Therapy; 6) Asthma; 7) Chronic Heart Failure; 8) Obesity; 9)Stroke—such as Acute Ischemia Again, each of the above listed conditionsis typically associated with one or more DRGs wherein stimulation of theassociated DRGs provides treatment or therapy. In some instances,Neuroregeneration Assisted Therapy for spinal cord injury also involvesstimulation of the spinal column.

It may be appreciated that the systems, devices and methods of thepresent invention may alternatively or additionally be used to stimulateganglia or nerve tissue. In such instances, the condition to be treatedis associated with the ganglia or nerve tissue so that such stimulationprovides effective therapy. The following is a list of conditions orindications with its associated ganglia or nerve tissue: 1) TrigeminalNeuralgia (Trigeminal Ganglion); 2) Hypertension (Carotid SinusNerve/Glossopharangyl Nerve); 3) Facial Pain (Gasserian Ganglion); 4)Arm Pain (Stellate Ganglion); 5) Sympathetic Associated Functions(Sympathetic Chain Ganglion); 6) Headache (PterygoplatineGanglion/Sphenopalatine Ganglion).

It may also be appreciated that the systems and devices of the presentinvention may also be used to stimulate various other nerve tissueincluding nerve tissue of the peripheral nervous system, somatic nervoussystem, autonomic nervous system, sympathetic nervous system, andparasympathetic nervous system, to name a few. Various features of thepresent invention may be particularly suited for stimulation of portionsof these nervous systems. It may further be appreciated that the systemsand devices of the present invention may be used to stimulate othertissues, such as organs, skin, muscle, etc.

It may be appreciated that although the lead is described herein aspositionable so that the at least one electrode is on, near or about atarget anatomy, at least one of the at least one electrode mayoptionally be positioned in the target anatomy.

Although the foregoing invention has been described in some detail byway of illustration and example, for purposes of clarity ofunderstanding, it will be obvious that various alternatives,modifications, and equivalents may be used and the above descriptionshould not be taken as limiting in scope of the invention which isdefined by the appended claims.

1. A method of treating a condition of a patient, wherein the conditionis associated with a portion of a dorsal root ganglion and is notsubstantially associated with other portions of the dorsal rootganglion, the method comprising: positioning a lead having at least oneelectrode so that at least one of the at least one electrode resides inproximity to the portion of a dorsal root ganglion; and providing astimulating signal to the at least one of the at least one electrode soas to stimulate the portion of the dorsal root ganglion in a manner thataffects the condition while not substantially stimulating the otherportions.
 2. A method as in claim 1, wherein the condition comprisespain.
 3. A method as in claim 1, wherein affecting the conditioncomprises alleviating the pain without causing a perceptible motorresponse.
 4. A method as in claim 1, wherein the condition is sensed bya patient at a location within a dermatome, and wherein the otherportions of the dorsal root ganglion are associated with other locationswithin the dermatome.
 5. A method as in claim 1, wherein the stimulatingsignal has a current amplitude of less than or equal to approximately 4mA.
 6. A method as in claim 5, wherein the stimulating signal has acurrent amplitude of less than or equal 1 mA.
 7. A method as in claim 1,wherein positioning the lead comprises advancing the lead using anepidural approach.